In various downhole tools such as for example casing drilling lock assemblies, packers etc., a pushing force along the axis of the borehole is required to set the tool and a straight pull along the axis is necessary to release the tool from its engaged position inside the borehole. In particular, some downhole tools include locking dogs that are driven out to engage casing, tubing or the borehole wall by axial movement of one structure on the tool such as a mandrel, relative to another member on the tool such as a housing. These locking dogs are released from engagement with the casing, tubing or the borehole wall by reverse axial movement of the tool structures.
An axial force generating tool is used to generate axial movement by gripping and axially pulling or pushing one structure upward or downward relative to the other. It will be appreciated that while pulling and pushing motion is required to actuate downhole tools, similar motion is required in other downhole applications such as to unstick a structure, for example sanded-in tubing, which is hung up down hole.
Generally, an axial force generating tool must be lowered on tubing such as drill pipe or coiled tubing that has enough strength to accommodate the stresses to move the structure axially upward (towards surface) or downward. Wireline, although easier and more cost effective to run in, cannot withstand much pulling force and cannot be used to exert a pushing force. Therefore, wireline is not generally used with an axial force generating tool.